1. Field of the Invention
This invention relates to meat marinating machines, and more particularly to a refrigerated cylindrical drum paddle-agitator mixer operated under a vacuum.
2. Description of the Prior Art
Methods and devices for marinating meat are many and varied. Early methods of deep marination include the injection of liquid via syringe. Advances over this method included the technique of massaging (or tumbling) meat under vacuum while exposing it to liquid marinade. In a vacuum, meat expands significantly and air may be extracted; the marinade then fills the interstices of the tissue in the hope that it will largely remain in place after the product is restored to normal atmospheric pressure. For larger pieces of meat, a combination of injection and vacuum massaging may be used for even distribution of the marinade.
Ordinarily, liquid marinades for meat are water based and contain additives to produce one or more results, including tenderizing, preserving, macerating, and/or flavoring. In the meat processing and packing industry, the challenge has been to get the liquid additives into the meat, distribute it evenly, and then keep it in the meat during processing or packaging. The first two of these challenges is partly addressed with vacuum tumbling. For example, in the ham industry the most common marinating machine is a vacuum tumbler comprising a vacuum drum having internal vanes. The drum is mechanically rotated about its horizontal axis. During this rotation, the meat is tumbled over the moving vanes causing the liquid to be "massaged" into the meat. In the poultry industry either a single or twin agitator is used. The meat is loaded into a horizontally positioned drum having a horizontal agitator shaft with fixed paddles. Under vacuum conditions, the paddles are rotated through the product, which massages liquid into the meat while massaging air out of the meat.
Industrial meat tumblers operated under vacuum are known in the art. These devices are adapted to thoroughly, uniformly, and efficiently expose meat to marinade, tenderizer, preservative, and/or flavoring prior to processing and packaging. An illustrative device is disclosed in U.S. Pat. No. 4,958,410, which discloses a machine for meat treatment and maceration comprising a rotatable drum with a hood inlet and means for automatically loading and unloading product through the hood inlet. U.S. Pat. No. 5,514,030, discloses a vacuum tumbler having an evacuatable drum mounted for rotation around its longitudinal axis, the drum having an opening at one end for loading and an opening at the other for unloading, and means for conveying material through the drum from the loading end to unloading end. The drum further has means for sealing the ends of the drum around the end openings to enable continuous passage of product into and out of the drum.
The problem has been, and remains, that over 50 percent of the liquid marinade routinely purges out of the meat during processing of the meat or after packaging. This occurs regardless of whether the meat is cooked before packaging, and it results in a compromised effect of the additives; i.e., reduced flavor, reduced longevity, and an unattractive appearance. Purging is particularly problematic when meat is cooked before packaging. Even vacuum massaged products lose most of the marinade introduced into the meat during processing.
In many existing marinating devices, the mechanical action of agitators and/or vanes imparts heat to the product, and heat causes liquid to purge out of the product after processing. It is not at all uncommon for the temperature of ham, which requires a lengthy four-to-five hour massaging cycle, to rise 12.degree.-15.degree. F. Poultry has a substantially shorter mechanical marinating cycle--only one half hour, typically--but still rises 2.degree.-3.degree. F.
A proposed solution to the problem of heat was advanced in the ham industry. It was discovered that when ham products are massaged at a temperature close to that of the freezing point of the marinade, the liquid became more stable in the meat matrix and purged in a lesser amount after processing. Thus, vacuum chilling became the accepted practice in the ham industry. The devices typically comprise a tumbling drum having a jacket through which refrigerant is circulated during the massage cycle. The meat product can be chilled to offset any mechanically induced heating.
Examples of combination vacuum chilling and tumbling devices, such as is described above, include U.S. Pat. No. 4,942,053, which teaches a vacuum chilling process for processing meat. U.S. Pat. No. 5,104,232, having a common inventor with the instant invention, teaches a vacuum tumble food mixer operable under vacuum conditions and having a chilling system. The disclosed device comprises a rotatable drum and a motor for rotating the same, and further includes vanes having a helical pitch for conveying product along the length of the drum from input to discharge openings. More recently, U.S. Pat. No. 5,564,332 discloses a massaging machine having a refrigerated processing tank and inlet and outlet chutes located at the same end of the tank. Paddles urge loaded meats away from the inlet chute and, when reversed, urge the meat towards the outlet chute.
While the principle of vacuum chilling and tumbling works well in practice in the ham industry, there is no similarly effective machine available for machine marinating poultry. For example, U.S. Pat. No. 5,564,332, described above, has insufficient heat exchange area per volume to chill certain meat products, most notably poultry, quickly enough for efficient processing. Because poultry massaging lasts only 20 to 25 minutes, there is not enough time for sufficient heat transfer to take place to reduce the temperature of the poultry product and thereby stabilize liquid marinade in the meat matrix. Therefore, there exists a need for a vacuum meat marinating machine adapted for use with products requiring a short vacuum massage cycle.